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Old 23rd June 2008, 06:15 PM   #21
smoking-amp is offline smoking-amp  United States
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Old 23rd June 2008, 06:47 PM   #22
oldeurope is offline oldeurope  Germany
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Default #10

Quote:
Originally #10 posted by kenpeter


Incomplete OT schematic without part values ...
I'm not sure which rail you prefer common to
power noise in this situation. Depends what
are you intending to drive in the next stage?

What was the trouble with Mu>1 and a resistive
divider??

---------------------------------------------------------

Nutz... I inverted twice.... Thats not helpful!

If I make the inverted triode behave as a follower
then overall Mu does not revert to 1 as intended.
I don't see an easy way to fix this.
Hi,
the schematic does not exist at the moment.
When it is finished, I'll make a new thread
about this pre.

@ kenpeter @ Don
I think the attachments from this thread
are interesting for you.

Isn't it possible to upload a 417Kb zip here?

Kind regards,
Darius
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Old 23rd June 2008, 09:49 PM   #23
Michael Koster is offline Michael Koster  United States
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Default #22,21

#22

"I think the attachments from this thread
are interesting for you."

Very interesting. The signal path outlined in red helps a lot

#21

Don, I think I follow and it looks like the same idea. No grid current... Here's my doodle along the same lines. I was thinking similar triodes but the slight mismatch is interesting. Or I may be off in the weeds

Cheers,

Michael
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Old 23rd June 2008, 11:22 PM   #24
Wavebourn is offline Wavebourn  United States
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Take any tube and select load resistance and idle current to get exactly unity gain. No feedback, the problem solved. However, without feedback it will be highly dependable on the tube used, but it is what you need. Tube gurus will be happy with your design creating new fashions and urban legends about different sounds of different tubes.
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Old 23rd June 2008, 11:34 PM   #25
jon_010101 is offline jon_010101  United States
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Quote:
Originally posted by Wavebourn
However, without feedback it will be highly dependable on the tube used, but it is what you need. Tube gurus will be happy with your design creating new fashions and urban legends about different sounds of different tubes.

So true! -- I would wire up a unity-gain plate follower and call it a day
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Old 24th June 2008, 12:38 AM   #26
smoking-amp is offline smoking-amp  United States
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"Here's my doodle along the same lines. I was thinking similar triodes but the slight mismatch is interesting." Ken

Looks good to me. Maybe want to upgrade those depletion mode CCS's to cascode ones for lower capacitance effects. Obviously this approach has a close parallel with Darius's fourth topology or triode transformer mode. But two tubes to get unity gain.....? (OK, I know, op. amps have dozens of transistors, and people still use them for unity gain at times.)

"Take any tube and select load resistance and idle current to get exactly unity gain. No feedback, the problem solved. However, without feedback it will be highly dependable on the tube used, but it is what you need. Tube gurus will be happy with your design creating new fashions and urban legends about different sounds of different tubes." Anatoliy

Definitely the obvious solution, but Darius apparently doesn't consider cathode degeneration as no-feedback. (or he would just use the usual split load concertina splitter) Not sure whether Darius would consider a low plate resistor alone to be linear enough. He should add to his "rules" that nothing can be done easily.

"I would wire up a unity-gain plate follower and call it a day" Jon

I'm afraid thats got obvious neg. feedback. (Bad boy. Go to jail!) We have to hide the feedback inside the tube Mu factor some how, unless you can come up with a stealth plate feedback resistor. How about a graphite mounting post (carbon arc rod) for the plate cap lead?

The pentode scheme (g2 driven) still seems the easiest way so far, to me. Or the beam deflector tube scheme. Wonder what Darius will come up with now for his preamp.

Don
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Old 24th June 2008, 01:11 AM   #27
smoking-amp is offline smoking-amp  United States
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How about just coupling the un-inverted signal to the following stage's cathode instead of it's grid. If current gain is required to do that, then put in a cathode follower or Mosfet follower with optional CCS pull-down. So simple, must be something wrong. Uh-Oh, I'll bet cathode followers are against the "rules" too.

Don
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Old 24th June 2008, 02:36 AM   #28
kenpeter is offline kenpeter  United States
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The triode has feedback between all three terminals. Even the plate
resistor presents a negative feedback. It is hard to call any triode
circuit (except perhaps the lower triode of a cascode) one without
negative feedback.

Oldeurope will have to define which modes of negative feedback are
acceptable, if we are to understand the rules of his game. So far he
has given us only intrinsic voltage feedback from the plate (resistor)
to work with. I take nothing else for granted.
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Old 24th June 2008, 03:12 AM   #29
kenpeter is offline kenpeter  United States
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The lower Triode in this bizarre cascode is INVERTED and Inverting.
The upper Triode in this cascode is cathode driven non-inverting.
Or at least I think it is??? Is overall Mu/Mu' now equal to 1???

Have I used any disallowed feedbacks?
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Old 24th June 2008, 03:18 AM   #30
SY is offline SY  United States
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How about disallowed biasing?
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